> ## Documentation Index > Fetch the complete documentation index at: https://developers.circle.com/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}. > Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts. > Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md. > Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md. > Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers. > Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews. > Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming. > Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md. > Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors. > API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product. > Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes. > When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records. > Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md. # How-to: Fund an agent wallet > Add USDC to your agent wallet using a wallet transfer or fiat onramp. Add USDC to your agent wallet before sending transfers or paying for services. This is a prerequisite for [transferring USDC](/agent-stack/agent-wallets/wallet-operations/transfer), [bridging USDC](/agent-stack/agent-wallets/wallet-operations/bridge), [paying for services](/agent-stack/agent-nanopayments/operations/pay-for-service), and other operations that spend USDC. ## Prerequisites Before you begin, ensure you have: * Installed [Node.js v20.18.2 or later](https://nodejs.org/). * Installed Circle CLI: ```bash theme={null} npm install -g @circle-fin/cli ``` * [Authenticated](/agent-stack/agent-wallets/wallet-operations/authenticate) your agent wallet. ## Steps Run `circle wallet fund` with your wallet address, blockchain, amount, and method (crypto or fiat). Replace `0xYourWalletAddress` with your wallet address. ```bash theme={null} circle wallet fund --address 0xYourWalletAddress \ --chain ARC --amount 10 --method crypto ``` The CLI prints a terminal QR code and an [EIP-681](https://eips.ethereum.org/EIPS/eip-681) deposit URI. Scan the QR code with your mobile wallet to send the funds. Pass `--export ` to save a PNG instead, or `--open` to render the QR code in a browser tab. ```bash theme={null} circle wallet fund --address 0xYourWalletAddress \ --chain ARC --amount 10 --method fiat ``` Your browser opens to the onramp provider where you can purchase USDC with a card or bank transfer. Pass `--no-open` to print the URL instead of opening the browser. To use testnet, replace `BASE` with a testnet blockchain (for example, `ARC-TESTNET`) and omit `--method` and `--amount`. On testnet, `circle wallet fund` draws 20 USDC from the Circle faucet. See [supported blockchains](/agent-stack/agent-wallets/supported-blockchains) for the full list. Check your balance to confirm the deposit: ```bash theme={null} circle wallet balance --address 0xYourWalletAddress --chain ARC ``` See the [CLI command reference](/agent-stack/circle-cli/command-reference) for full syntax and options, including `--token` to fund with ETH or native tokens.